Radio frequency drying device



Nov. 18 1952 R REED ETAL 2,618,733

RADIO FREQUENCY DRYING DEVICE Filed Oct. 26, 1948 2 SHEETS-SHEET 1 8 & PLATE VOLTAGE TIMING POWER 6/ I SUPPLY SWITCH OSCILLATOR L w I L T? F'IG.

FIG. 2 9

INVENTORS BUCKLEY R. REED ARNOLD H. CROWLEY ATTORNEY Nov. 18, 1952 R REED ETAL 2,618,733

RADIO FREQUENCY DRYING DEVICE Filed Oct. 26, 1948 I 2 SHEETS-SHEET 2 -%DUCTIO!+ MOTOR N VE N TOPS BUG/(LEV I? REED ARNOLD H. CROWLEY ATTORNEY Patented Nov. 18, 1952 D- STAT ES ENT 0 FF 1 CE RADIO FREQUENCY DRYING, DEvIcE' Buckley R}. Reed-,Newton, and A'rnold HrCrowley,

Walth'am, Mass, vas'signorsi to Ra-yth'eon Mann'- facturing; Gompany Newton, Mass, at corporation of Delaware Application October-26, 1948', SerialNo. 56,525

3' Claims. l

Thisinvent-lon relates to the heating of material hy'radio frequency currents, and more particularly to the use of such radio-frequency heati'ng-for the drying ofmolds, commonly known as mats, used in the newspaper industry-r In the newspaper'printing industry, the molds in which'thefinal plates for printing newspapers are cast are made of fibre which i'sfirst moistenedi and thenim'pressed withthe desired letters and figures in order to form the requisite mold for casting" the print metal. The moistening process i's necessary in' order' that a deep,- sharp impression may be acquired with. a minimum of pressureon theimpressing plate. After this process is' com leted; the-moldor; as is commonly k n'own in" the industry, the mat, is dried, and,

since the printing industry requires that this entire process" be completed as rapidly as possible, this-drying process should be accomplished in a matter ofmi'nutes;

Previously the" drying was accomplished by placing the mats in dryers which were heated, thus drying the mat by applyingheat on the outer surfaces thereof causing the moisture toevaporate as steam: This has two disadvantages. Firstly; it takes a considerablelength of time,

and, secondly, it dries from the out'sidein', thus producing a hard' outer surface which tends to hold the moisture on the inside, similar tothe manner'in which aloaf of'brea'd remains soft on the inside" while becoming crusted on-the outside during cooking-L Accordingly; it 'i'san object of the presentinvention' to produce a-d-i'ying device which willdry' the mats in a 'very short period" of time.

It isa further object-of this invention toprodiic'el a: device which will' dry the mat uniformly throughout.

Another object ofthis invention is to produce ase't 'of electrodes-which'willhold the mat dur-- ing' the drying'proces's so that'the mat will not warp.

Anotherobject of" this inventioni's'to provide a device'whe'rein the mat may be easily inserted and extracted from the'drying'machine: I

In. accordance with our invention; we" have? in the following specification disclosed and in the accompanying drawings illustrated the" various Fig.3 discloses the detailsof the linkage mech-' anism whereby both electrodes are simultaneously moved to engage and disengage the work; and

Fig; 4 represents another embodiment of our invention,' wherein endless belts carry the mats between the electrodes.

Referring now to Fig. l,there is shown a-power oscillator 3 which may' be of any well-known design, such as, for example, a Hartleyoscillator, which-feeds a pair'ofelectrodes diagrammatically shownas 4.- In order to control the'amount of time involved in anyone drying operation, and thereby control the extent of the drying, thereis utilized a timing'switcli 2 which energizes the: plate on the power oscillator tube by means of aplate voltage supply l for a certain length of time which maybe adjusted by the operator.

Each of the electrodes 4', as is more clearly shown in Fig. 2, ismadeup of a-series of parallel conducting rods 5 coated with a dielectric insulating material as at 6. These rods are maintained at a uniform potential throughout by means of asystem of strapping bars I to which isattach'ed a-power lead of the oscillator. 3.

Iii-series with this power lead there is a con-- the first one, but is attached to ground rather than to the power oscillator such that a radiofrequency potential maybe applied across the twoelectrodes 4.

The'parallel rods of the electrode 4 are rigidly supported by means of insulating'strips 9 which arepositioned at'righ-t angles to said conducting rods; 'I'hese'st'rips' 9-have holes in one edge and spaced along their length through which the rods 5 pass and" by which theyare firmly held.

Theaforesaidinsulating strips are held rigidly I Hi" in both sets of insulating strips whereby theymay-'befitted together inform a lattice ot squares. v

It may be seenthat thisopen lattice construction creates an electrode structure which will 'allow the steam, from the mat being dried", to

escape very easily through the-holesbetween the insulating strips;

The exact" form of the insulating holder is not I importantas longas'ittrigidly supports" the con'-' ductingrods trend will all'owthe esca'p'eme'nt of 3 the steam from the work. While in the applicants device these insulating strips are made of wood and the sleeves around the rods are made of glass, any material which is a good insulator may be used and which has the requisite strength and resistance to heat.

As shown in Fig. 1, the two electrodes t are positioned opposite each other such that the con ducting rods of both electrodes are parallel to each other, and each rod of an electrode is positioned such that it is directly opposite the middle of the space between two of the rods of the opposite electrode. By thus alternately positioning the parallel rods of the opposite electrodes, a path between the electrodes is obtained which is longer than the distance between the electrodes, and, moveover, each electrode has a path which goes to two of the rods in the opposite electrode.

It is possible to construct an electrode from a simple sheet of conducting material which will allow steam to pass through it, such as a piece of screening. A model of this type has been built and tested; however, such an electrodeis inclined to give uneven heating and warping of the mat. This occurs because the mat, after it has been impressed with the necessary letters and prints, possesses an uneven surface, and those portions of the surface which contact a continuous electrode over a large area tend to remain moist since they are, in eifect, shorted out by the electrode traveling along their surface, with the result that no heating current passes through that area. Furthermore, a higher heating current is required.

In the embodiment of the invention as shown in Fig. 2, contact is made with the work at specific discrete intervals and the intervals and henceforth current paths between the electrode elements are constant in length with a resultant uniformity of heating.

In order to prevent arcing between the work and the electrodes at the points adjacent to the contact of the electrodes to the work, insulating sleeves of glass are put over the parallel rods. The electrical energy is now fed into the work by means of the capacitance which exists between the work and each parallel rod with the glass sleeve acting as the dielectric between two capacitance plates, namely, the rod and the work. After the energy has been introduced into the work, it proceeds through the work to another point adjacent an opposite rod of the opposite electrode, and heats the work by a well-known dielectric heating effect wherein the moist mat acts as a semi-conductor. The electrons of each molecule of the mat are stressed first in one direction and then in the opposite direction in'response to the pull of the electrostatic field of the alternating voltage applied to the electrodes, and the resulting minute movement of said electrons and molecules creates heat by friction thereby heating the work.

Referring now to Fig. 3, there is showna structure whereby the pair of electrodes are moveably positioned with respect to each other such that the work may be inserted between them and then the electrode, an arm being positioned adjacent each of the four corners of each electrode.

Thus it may be seen that the two electrodes may be moved laterally while at all times remaining parallel to each other. Further, as the supporting arms swing in an arc, the distance between the electrodes is increased or decreased depending on the direction of movement. The electrodes 4 are linked to doors l3 which are hinged to the front part of the frame H which may be closed to create, together with frame II, a relatively confined space about the electrodes, and opened to allow insertion and removal of the mats. This link between the doors and the electrodes consists of short bars l4 which are attached to the front edge of the electrode and to approximately the middle of the door. When the doors are opened, the electrodes are moved outward and apart to allow the work to be more easily inserted and removed. As the doors are closed, the electrodes move inward and into closer proximity to each other, thus clamping the work to prevent warping.

In order to cause both doors to open and close simultaneously, there is provided a synchronizing mechanism which consists of a pair of bars [5 which are attached to the upper and lower edges of each door in the following manner. At points above and below the electrodes so that they will not interfere therewith a bar is attached to each door close to its swinging edge by means of a pivot pin. The other ends of a pair of bars, one from each door, are attached together by means of a bolt I5 and said bolt is slida-bly mounted in a slot I? cut in the machine frame such that when the doors are closed the two bars push the bolt inward along the slot, and, when the doors are opened, they pull bolt outward along the slot.

Thus it may be seen that the electrodes will move in and out in parallel relation to each other and with no relative lateral movement between said electrodes, but with relative transverse movement between said electrodes, such that the space between them is increased or decreased as the case may be. This facilitates insertion and removal of the mats in the space between the electrodes.

In Fig. 4 there is shown another embodiment of the invention, wherein the electrodes 4 are curved plates, with the parallel conducting members positioned in the same manner as previously described for the electrodes shown in Fig. 2. In general use the mats must eventually be curved to conform to the shape of the roll presses for which they are used to mold the plates. If they are not curved during the drying process, they must later be curved by some form of clamp to create the correct contour. It is, therefore, not essential that in this embodiment the plates be curved, and, moreover, it is not essential in the embodiment as shown in Fig. 2 that the plates be flat.

. At the opposite end of each electrode there are positioned rollers l 8 upon which there is mounted an endless belt which may be of any material which will withstand the required temperature and has good insulating properties, and is flexible. The tension on these belts is adjusted and maintained by idler rollers l9 which are moveably positioned such that, by adjusting their position, the overall length of travel of the endless belt may be varied. The rollers are driven by means of a pair of gears 20 which are attached to the rollers at one end of the electrodes. These gears are driven by a mechanical coupling from azmotor 2| through a suitable gear reduction unit It may thus be seen that, when a piece of Work such as the mat 23 is fed into one edge of the space between the electrodes, between rollers 18, the endless belts will carry the work on through the electrodes, and, if the speed is adjusted correctly, the time required for the work to travel the distance between the electrodes will be just that required to dry the work a sufiicient amount. The tension on the endless belts will exert a lateral pressure on the work thus keeping it from warping. Furthermore, since the work is passing through the electric fields between the parallel rods of the electrodes, it will pass through any high as well as any low intensity spots of said field, thus insuring an extremely even heating of the work.

It may be pointed out that a feature of this process is the uniform drying of the sheets obtained Whether the sheets are put in relatively moist or relatively dry, since if they are moist more current is drawn from the oscillator and more heat is created in the work thus driving the steam out faster such that the end result is that the work comes out at a uniform dryness. Similarly, if a piece of dryer work is put in, less current flows through the work creating less heat, and, as a result, less drying, thus creating as aforestated a uniformity of dryness between the different pieces of work. It is to be clearly understood that while we have disclosed one type of electrode structure using parallel conductor rods, any electrode structure which creates the uniform field between the plates may be used as an electrode. For example, the rods might be circular in shape.

The frequency of operation of this equipment is not critical, but depends upon the design of the particular structure involved. For example, if wire screens were used for the electrodes, as has been previously done in experimental models, a frequency of around 6 to 8 megacycles is convenient and practical. With the present design a frequency of approximately 14 megacycles is being used, but it would be possible to vary this frequency from to 20 megacycles and even considerably above and below this range without seriously affecting the operation of the device.

It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. In an electrical material heating device, a plurality of electrodes, means for energizing said electrodes with radio frequency energy, and means for moving said electrodes apart, to insert and remove the material to be heated, said means producing a lateral motion in the electrodes, said electrode moving means comprising pairs of arms, pivotally mounted to the electrode, and to the frame of the drying device, and other arms pivotally linked to said electrodes, and with their opposite ends pivotally connected together, and restricted to motion in only a direction parallel to the direction of lateral motion of the electrodes.

2. In an electrical material heating device, a plurality of electrodes, each of said electrodes comprising a plurality of parallel conducting members, each of said parallel conducting members being surrounded by a sleeve of insulating material, means for energizing said electrodes with radio frequency energy, and means for moving said electrodes apart, to insert and remove the material to be heated, said means producing a lateral motion in the electrodes, said electrode moving means comprising pairs of arms, pivotally mounted to the electrode, and to the frame of the drying device, and other arms pivotally linked to said electrodes, and with their opposite ends pivotally connected together, and restricted to motion in only a direction parallel to the direction of lateral motion of the electrodes.

3. In an electrical material heating device, a plurality of electrodes, each of said electrodes comprising a plurality of parallel conducting members, each of said parallel conducting members being surrounded by a sleeve of insulating material, each member being positioned directly opposite the middle of the space between a pair of members of the opposite electrode, means for energizing said electrodes with radio frequency energy, and means for moving said electrodes apart, to insert and remove the material to be heated, said means producing a lateral motion in the electrodes, said electrode moving means comprising pairs of arms, pivotally mounted to the electrode, and to the frame of the drying device, and other arms pivotally linked to said electrodes, and with their opposite ends pivotally connected together, and restricted to motion in only a direction parallel to the direction of lateral motion of the electrodes.

BUCKLEY R. REED. ARNOLD H. CROWLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,079,708 Hart May 11, 1937 2,112,418 Hart et al Mar. 29, 1938 2, 33,176 Melton et al. Feb. 25, 1941 2,288,269 Crandell June 30, 1942 2,304,958 Rouy Dec. 15, 1942 2,319,174 Wilson May 11, 1943 2,325,950 Greene et al. Aug. 3, 1943 2,390,572 De Brabander Dec. 11, 1945 2,402,609 De Brabander June 25, 1946 2,409,431 Hess Oct. 15, 1946 2,422,979 Pecker June 24, 1947 2,442,451 Albin June 1, 1948 2,442,986 Ransburg June 8, 1948 2,453,185 Bilhuber Nov. 9, 1948 2,457,498 Russell et al. Dec. 28, 1948 2,460,566 Brown et al. Feb. 1, 1949 2,473,251 Hsu June 14, 1949 2,477,214 Story July 26, 1949 2,483,623 Clayton Oct. 4, 1949 2,512,311 Davis June 20, 1950 2,560,903 Stiefel July 17, 1951 OTHER REFERENCES Winlund, Electronic Heating, Electronics, May 1946, pages 108-113. 

